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Abstract: Mound spring structures composed of tufa precipitated from near-ambient temperature spring waters are rare; consequently, the hydrochemical evolution of the water and the processes that control carbonate deposition in these systems are not well understood. This study analysed the water from 3 mound springs in an arid environment in the vicinity of Lake Eyre South, South Australia. Samples were tested for major ion chemistry and stable isotope ratios of water (2H/1H and 18O/16O). Most CO2 degasses from water (i) before emergence as it ascends in the fracture-derived spring conduit system below the spring opening and (ii) after emergence in the turbulent upper tail environment between the spring vent pool and the tail delta. However, modern carbonate precipitation was generally restricted to tail delta environments, spatially disconnected from the areas of strongest CO2-degassing. In addition to CO2-degassing and carbonate precipitation, evapotranspiration and heterotrophy were inferred to be processes controlling the chemical evolution of water flowing through the tail delta. Based on considerations of the geometry of the tail delta and evapotranspiration rates, it was inferred that infiltration is an important process in determining the tail delta size and hence the morphology of the mound spring environment. A reactive transport model was used to assess the importance of these processes for the evolution of carbonate hydrochemistry. The model outcomes showed that water loss via evapotranspiration does not significantly affect tufa precipitation, despite the springs being located within an arid environment. Heterotrophy was considered in the model in order to reproduce observed pH and carbonate concentrations, highlighting the role of vegetation in controlling the water chemistry. The modelling approach adopted here provides a generic framework for the analysis of calcareous spring deposits and places quantitative constraints on data-based process conceptualisation. [Copyright &y& Elsevier]

Summary: Hydrogen and oxygen isotopes of water are common environmental tracers used to investigate hydrological processes, such as evaporation, vegetation water use, surface water–groundwater interaction, and groundwater recharge. The water isotope signature in surface water and groundwater evolves from the initial rain signature. In mountain terrain, rain water stable isotope composition spatially varies due to complex orographic precipitation processes. Many studies have examined the isotope–elevation relationships, while few have quantitatively investigate the terrain aspect and slope effect on rain isotope distribution. In this paper, we examine the orographic effects more completely, including elevation, terrain slope and aspect, on stable isotope distribution in the Mount Lofty Ranges (MLR) of South Australia, using a multivariate regression model. The regression of precipitation isotope composition suggests that orographic effects are the dominant controls on isotope spatial variability. About 75% of spatial variability in δ 18O and deuterium excess is represented by the regression using solely orography-related variables (elevation, terrain aspect and slope), with about 25% of δ 18O spatial variability attributed to the terrain aspect and slope effect. The lapse rate is about −0.25‰ for every 100m at both windward and leeward slopes. However, at the same elevation, δ 18O at the leeward slope (eastern MLR) is 0.5‰ larger than that at the windward slope. The difference can be explained by different mechanisms – continuous rain-out processes on the windward side and sub-cloud evaporation on the leeward side. Both δ 18O and deuterium excess maps (1km resolution) are constructed based on the regression results for the MLR. Both maps are consistent with groundwater of local precipitation origin, and useful to examine groundwater recharge. [Copyright &y& Elsevier]

Highlights: [•] We raise an issue that has not been considered in chloride mass balance method. [•] Chloride depositions in throughfall were collected in eucalyptus and pine plantations. [•] Chloride depositions were modelled both mechanically and empirically. [•] The modelling can quantify the contribution of wind speed, rainfall, etc. [•] The model can explain both temporal and spatial variation of throughfall deposition. [Copyright &y& Elsevier]

Abstract: The mound springs of the Lake Eyre South region of South Australia are rare but prominent, dome-shaped accumulations of largely calcium carbonate deposited by artesian springs. Despite similar formations being found worldwide, few intensive studies of the formation and ongoing evolution of these structures exist. In this study, samples from a selection of active mound springs were subjected to petrological and Scanning Electron Microscopy (SEM) techniques to gain insight into mound spring morphology. Additionally, microcosms containing three types of artificial substrate (marble, glass and copper) were placed within active mound spring environments to aid determination of the rate, spatial extent and the influence of microbial activity on carbonate precipitation. Finally, water samples from spring vents were analyzed for water quality and major ions. Carbonate deposits were interpreted to be largely plant or microbial tufa. From the microcosms, thrombolitic-textured micrite was deposited on only the marble and glass substrates and only within spring tails distal from vents. Precipitation rates from the microcosm experiment of between 0.15 and 1.6kgm−2 yr−1 are similar to rates observed at cyanobacteria-associated, low-energy, carbonate depositing environments. These results suggest that tufa precipitation is linked to the development of extracellular polymeric substances. Conversely, it was interpreted that emergent spring water is calcite under-saturated based on water chemistry analyses and marble dissolution proximal to spring vents. A number of factors important to the formation of mound springs were determined; including the role of bio-mineralization and hydrophytes in mound construction and the implications for time-limited and spatially dynamic precipitation on spring flow. [Copyright &y& Elsevier]

Abstract: The input of groundwater-borne nutrients to Adelaide''s (South Australia) coastal zone is not well known but could contribute to the ongoing decline of seagrass in the area. As a component of the Adelaide Coastal Waters Study (ACWS), the potential for using the radium quartet (223Ra, 224Ra, 226Ra and 228Ra) and 222Rn to evaluate submarine groundwater discharge (SGD) was evaluated. Potential isotopic signatures for SGD were assessed by sampling groundwater from three regional aquifers potentially contributing SGD to the ACWS area. In addition, intertidal groundwater was sampled at two sand beach sites. In general, the regional groundwaters were enriched in long-lived Ra isotopes (226Ra and 228Ra) and in 222Rn relative to intertidal groundwater. Radium activity (but not 222Rn activity) was positively correlated to salinity in groundwater from one of the regional aquifers and in intertidal groundwater. Radium isotope ratios (223Ra/226Ra, 224Ra/226Ra and 228Ra/226Ra) were less variable than individual Ra isotope activities within potential SGD sources. Recirculated seawater (estimated from the intertidal groundwater samples with seawater-like salinities) also had distinctly higher Ra isotope ratios than the regional groundwaters. The activities for all radioisotopes were relatively low in seawater. The activity of the short-lived 223Ra and 224Ra were highest at the shoreline and declined exponentially with distance offshore. In contrast, 228Ra and 226Ra activities had a weak linear declining trend with distance offshore. Rn-222 activity was at or near background in all seawater samples. The pattern of enrichment in short-lived Ra isotopes and the lack of 222Rn in seawater suggest that seawater recirculation is the main contributor to SGD in the ACWS area. Preliminary modeling of the offshore flux of 228Ra and 226Ra suggest that the SGD flux to the ACWS area ranges between 0.2 and 3·10−3 m3 (m of shoreline)−1 s−1. [Copyright &y& Elsevier]